Faucet without mixer? Only hot/cold?

  • Erstellt am 2016-07-22 21:31:59

Sir_Kermit

2016-07-24 16:29:45
  • #1
Hi,



However, the desired final temperature depends on the temperatures of cold/hot water and can be calculated using the mixing rule. Anyway, from an energy perspective, it initially does not matter how I achieve my desired temperature. It is primarily about the specific heat capacity of water and the required temperature differences for a desired amount (mass) of shower water. Example: I need 1 kg of water at 40 degrees and must raise the temperature by 30 degrees (assume the water supply temperature is 10 degrees). How I get there, with or without mixing, is always tied to the same amount of energy in joules, namely 30 x 4187 J. That is the bare theory, which you can test online with a mixing calculator.
For 1 kg of 40-degree warm water, you need 0.6 kg of water that you heat from 10 to 60 degrees and 0.4 kg of water at 10 degrees.
In the first case, it is 30 x 4187 joules; in the mixing case, it is 0.6 x 50 x 4187 joules.

What is not indifferent, however, are changes in efficiency (when starting the systems) and losses. But these depend heavily on the type of usage and the constructive design of the water supply in the house.
See the post by

Kermit
 

daniels87

2016-07-24 16:41:49
  • #2
That was purely related to the fittings. I don’t understand why it should be better to use only hot or cold water.

Since we don’t have a circulation line, I also have a small regulated instantaneous water heater for the bathroom sinks that heats up until warm water arrives on the upper floor.
1. Do I then always have to wait, and
2. doesn’t the entire pipe from the basement to the upper floor fill up with warm water, which then cools down in the pipe? In winter it doesn't matter since it stays within the thermal envelope, but outside the heating period it’s a loss. However, this is probably negligible.
 

Sir_Kermit

2016-07-24 17:13:13
  • #3
Hello,


If the temperature is fixed, then you can blindly turn it to hot and it fits. Maybe quite useful after a heavy evening party. Whether you should generally do without a mixing valve is up to everyone; I would definitely install one. From that point of view, there would be no "digital" water with us either. And the tap water is around 9 to 15 degrees, depending on the region, so it could sometimes be too cold. IIRC, the original poster only meant the shower. Then cold showers must simply never happen.

A supply temperature of 60 degrees can pose a risk for experimentally inclined younger children. Here, limiting the temperature would be useful.
 

Elina

2016-07-24 18:12:14
  • #4


I have to correct you there. If you don’t fully open the hot water tap, no hot water will come out at all because the tankless water heater won’t even start. It’s electronic, not hydraulic, but it still requires a minimum flow rate to activate. For things like quick handwashing, I only use cold water anyway, since it takes a few liters before the warm water even arrives. The eco-friendly part of me also makes sure not to set the water hotter than absolutely necessary. With a storage heater, you probably have a temperature of 60°C and then mix it down to 40°C or whatever you need. On top of that, there are the heat losses. My tankless water heater only makes these 40°C from the start, unless I absolutely want 60°C. Besides the energy saved by less heating, you also save on storage losses.

@Saruss, did you include this item in the 20-day calculation? Meaning that the tankless water heater has to heat less powerfully from the start?

By the way, I finally found something I like even better with the term "two-handle faucet," namely the "three-hole faucet," where you really don’t have any cranks anymore but rather levers or push-buttons as desired, and you can install those completely independently somewhere, for example in the wall.
 

Elina

2016-07-24 18:58:46
  • #5
Attempt at my own calculation:

An instantaneous water heater with 18 kW consumes about 9 kWh per hour of showering. At this point, I don’t understand why calculations on the internet, which I found via Google, are based on the maximum power of the instantaneous water heater. No one showers with 60°C hot water... so I calculate with 40°C, meaning the instantaneous water heater only needs 50% of its power.
Edit: I checked it out. The instantaneous water heater still only runs at 3.5 kW when showering. Since our electricity consumption is recorded, a look at the balance chart when showering occurs at 4 a.m. is enough, as then only the instantaneous water heater consumes electricity. Maybe this has something to do with the rather low water flow rate, since the lower the water flow, the less energy is consumed. In any case, another reason not to assume the maximum power of the instantaneous water heater!

We shower together about 10 minutes per day. That makes 70 minutes per week, which would be around 10 kWh per week, 520 kWh per year. Plus a few kWh for cleaning water; washing up does not require water from the instantaneous water heater.
This roughly agrees with our experience regarding electricity bills from the last 4 years.

All of this still needs to be related to water consumption. According to various statistics, the share of hot water is about 30%. For us, that would be 10 cubic meters per year and 27 liters per day. Somehow quite low. I assume that “share of hot water” means water at 60°C; normally cold water is mixed in during showering, so I wouldn’t equate 27 liters of “hot water” in our case with 27 liters of “shower water.” In an average case, 27 liters of hot water would rather result in 50 liters of shower water. Then it makes sense.

However, I doubt that any electricity could be saved here by using another type of hot water generation. But a comparison would only be possible if one had a similar hot water consumption as we do.
 

Elina

2016-07-24 19:18:26
  • #6
It is even easier.... had a board in front of my head. Called up the power consumption meter. Current consumption 230 W (computer, base load). Then turned on hot water (40°) in the shower, looked at the meter again. Consumption: 5 kW. Turned off the tap again, looked at the meter again: 230 W.

The instantaneous water heater therefore runs at about 4.7 kW when showering at 40°. Minus the high power of the pressure boosting system so that water comes out of the pipe at all. This is 500 W (determined with the same method, but with the cold water tap). So purely for the instantaneous heater remains 4.2 kW of the 18 kW maximum output.

 

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